Cracking hydrocarbon residua to coke and aromatic gas oil

ABSTRACT

COKE AND A GAS OIL FRACTION BOILING BETWEEN 400 AND 10500*F. ARE PRODUCED BY HYDRODEPOLYMERIZING A HYDROCARBON RESIDUA. IN PARTICULAR A STEAM CRACKED TAR HAVING A BOILING POINT ABOVE 6500*F., WITH A SUBSTANTIAL AMOUNT OF THE TAR HAVING A BOILING POINT ABOVE 10050*F., IS MIXED IN SPECIFIC PROPORTIONS WITH A GAS OIL HAVING A BOILING POINT BETWEEN 400 AND 650*F. AND AN ACYCLIC HYDROCARBON MODIFIER IN A REACTION ZONE OPERATING AT A TEMPERATURE BETWEEN 775 AND 900*F. AND AT A PRESSURE BETWEEN 50 AND 1000 P.S.I.G. TO MAXIMIZE THE AMOUNT OF COKE PRODUCED.

United States Patent No Drawing. Continuation-impart of application Ser.No.

840,814, July 10, 1969. This application Jan. 13, 1971, Ser. No. 106,278

Int. Cl. Cg 37/06 US. Cl. 208-46 Claims ABSTRACT OF THE DISCLOSURE Cokeand a gas oil fraction boiling between 400 and 1050 F. are produced byhydrodepolymerizing a hydrocarbon residua. In particular a steam crackedtar having a boiling point above 650 F., with a substantial amount ofthe tar having a boiling point above 1050 F., is mixed in specificproportions with a gas oil having a boiling point between 400 and '650"F. and an acyclic hydrocarbon modifier in a reaction zone operating at atemperature between 775 and 900 F. and at a pressure between 50 and 1000p.s.i.g. to maximize the amount of coke produced.

RELATED APPIIICATIONS This is a continuation-in-part of Ser. No.840,814, filed July 10, 196-9, now abandoned.

BAOKGROU ND OF THE INVENTION This invention relates tohydrodepolymerizing a hydrocarbon residua to produce coke and a gas oilfraction boiling between 400 and 1050 F.

It is expected that steam cracking facilities will expand in the future,particularly in Europe. This will require means for easily disposing ofthe considerable amounts of tar which are a concomitant part of thesteam cracking process. One obvious method is to up grade these tars aswell as other residuas by thermally treating the tars with a hydrogendonor diluent material. The donor diluent is a hydrogen-containingmaterial, aromaticnaphthenic in nature, that has the ability to take uphydrogen in a hydrogenation zone and readily release it to ahydrogen-deficient oil in a thermal cracking zone. Unfortunately,however, there is often undesired coke deposition and creation of hotspots in preheater zones, leading to plugging of the equipment.

In pending application Ser. No. 29,629, filed Apr. 17, 1970 for Ralph B.Mason and Glen P. Hamner there is described and claimed a process fortreating hydrocarbon residua, a particular steam cracked tar, to produceprimarily an aromatic gas oil. However, under the process of thisinvention very little coke is produced.

It is an object of this invention to produce a low sulfur content cokeproduct by hydrodepolymerizing a hydrocarbon residua such as steamcracked tar.

SUMMARY OF THE INVENTION It has now been found that coke yield can bemaximized when desired by mixing in a reaction zone 50 to 80 weightpercent of a hydrocarbon material having a boiling point above 650 F.(heavy gas oil+hydrocarbon residua fraction) with to 50 weight percentof a hydro carbon material having a boiling point between 400 and 650 F.(light gas oil) together with 1 to weight percent of an acyclichydrocarbon modifier wherein the reaction zone is operated at atemperature between 775 and 900 F., and a pressure between 50 and 1000p.s.i.g.

In a preferred embodiment of this invention the noncoke product producedin the above process is separated into a hydrocarbon fraction having aboiling point be- 7 3,725,242 Patented Apr. 3, 1973 tween 400 and 650F., a hydrocarbon fraction having a boiling point between 650 and 1050F. and a hydrocarbon fraction having a boiling point above 1050 F. sothat the hydrocarbon fraction having a boiling point above 1050 F. maybe recycled to the reaction zone along with that portion of thehydrocarbon fraction having a boiling point between 400 and 650 F.necessary to maintain the 20 to 50 weight percent in the reaction zone,and either recovering or recycling the hydrocarbon fraction having aboiling point between 650 and 1050 F.

PREFERRED EMBODIMENTS OF THE INVENTION In accordance with the present.invention a hydrocarbon residua having a boiling point above 650 F. witha substantial amount, preferably more than 30 weight percent, of theresidua having a boiling point above 1050" F. is mixed with a gas oil,then introduced into a reaction or depolymerizing zone where the mixtureis contacted with an acyclic hydrocarbon modifier under specifiedconditions. Alternatively, all of the above could be mixed together atthe same time in the reaction or depolymerizing zone instead of asabove.

Suitable hydrocarbon residua would include thermal tar from steamcracking, catalytic clarified oil, reduced crude, shale oil residua,liquefied coal fractions and other similar materials, but mostpreferably steam cracked tar, catalytic clarified oil or otherhydrocarbon residua which have an aromatic content greater than about 70weight percent since these residua are highly hydrogen deficient.Because these materials are generally too viscous to be handled easily,it is necessary to add a solvent such as gas oil to reduce theviscosity. This permits easy pumping at moderate temperatures andprevents coking at hot spots in the system. It is preferred that a lightgas oil (i.e., a gas oil having a boiling point between 400 and 650 F.)be used as the solvent, but heavy gas oils (i.e., gas oil having aboiling point between 650 and 1050 F.) may also be used, provided thatthere is 20 to 50 weight percent, based on the feed to the reactionzone, light gas oil in the mixture.

Since it is desired to maximize the coke yield, it is preferred thatonly enough light gas oil is needed as a solvent be used since thehigher boiling range fractions contain more Conradson carbon or cokeprecursors. Therefore, 20 to 35 weight percent of light gas oil ispreferred.

This mixture of gas oil and hydrocarbon residua is then maintained in aliquid phase in a reaction zone operating at a temperature between 775to 900 F., preferably 780 to 800 F., and at a pressure between 50 and1000 p.s.i.g. An acyclic hydrocarbon modifier is jetted, sprayed orotherwise thoroughly mixed and passed through the liquid in the reactiondone.

Suitable acyclic hydrocarbon modifiers would include parafiins of 4 to10 carbon atoms per molecule or their isomers which have boiling pointsless than 350 F. Preferred examples of such modifiers are heptane andits isomers; hexane and its isomers; n-pentane; and 2,4,4- trimethylpentane because of the valuable by-products produced when they are used.When n-heptane is the modifier n-butane, n-pentaneand n-hexane are thevaluable by-products formed. On the other hand, if isoheptane is themodifier iso-butane, iso-pentane and isohexane are formed. If n-hexaneis mixed in the reaction zone n-pentane and n-b-utane result. Likewiseif isohexane is the modifier iso-pentane and iso-butane is formed. Whenn-pentane is used n-b-utane is formed. The

use of 2,2,4-trimethyl pentane unexpectedly results in the production ofthe important blending agent, triptane.

Other suitable modifiers are olefins and diolefins of similar skeletalconfiguration, heavy alkylates and the 210-400 F. fraction made bypolymerizing propylene and butylene with H PO on kieselguhr [HydrocarbonProcessing, v. 47:170 (September 1968)], and the like.

Without intending to limit the invention to any area of what occurs, itis believed that the mechanism is one in which the modifier is beingconsumed with accompanying hydrogen exchange, demethanation, alkylation,isomerization, aromatic disproportionation and probably every knownhydrocarbon reaction. The most plausible explanation is a free radicalmechanism in which the condensed ring aromatic compounds of the tardepolymerize with the formation of free radicals which attach themselvesto the modifier as a sink. In doing so the modifier in turn forms freeradicals involving stepwise degradation and rearrangement reactionsleading to gaseous products and coke.

It has been found that to maximize coke yield these modifiers must beadded in amounts of about 1 to 20 weight percent based on thehydrocarbon residua, preferably between about 5 and weight percent.Under the operating conditions the hydrocarbon modifier remains in thevapor phase and has a residence time of between 5 and 60 minutes onthrough the liquid in the reaction zone. During the time the modifierremains in the reaction zone a portion of it is consumed and is themajor source of the coke formed which remains suspended in the liquid.Thus increasing the residence time aids in this conversion to coke. Forthis reason a temperature of about 780 F. and a residence time of about60 minutes is preferred. If the temperature is increased, then theresidence time must be decreased in order to maintain maximum cokeyield. If the residence time is increased, the temperature is decreased.

It has also been found that small amounts of oxygen added to themodifier as it enters the reaction zone results in an increase in theamount of coke produced. The amount of oxygen added is very small,generally on the order of less than 100 parts per million of fresh tarfeed and preferably less than 50 parts per million. At the preferredtemperature of about 780 F. 25 parts per million of oxygen should beadded.

In a preferred embodiment of the invention the products produced in thereaction zone are removed after an appropriate time and introduced intoa fractionator where the product is separated into a fraction containingthe modifier, a hydrocarbon fraction having a boiling point between 400and 650 F., a hydrocarbon fraction having a boiling point between 650and 1050 F., hydrocarbon fraction having a boiling point above 1050 F.and coke.

The modifier and the hydrocarbon fraction boiling above 1050 F. arerecycled to the reaction zone along with that portion of the hydrocarbonfraction boiling between 400 and 650 F. necessary to maintain the to 50weight percent of such fraction going into the reaction zone. Theremaining portion of the hydrocarbon fraction having a boiling pointbetween 400 and 650 F., along with the coke and light products boilingbelow 400 F. may be recovered. The hydrocarbon fraction having a boilingpoint between 650 and 1050 F. may be either recycled to the reactionzone or recovered as desired.

The following example is included to illustrate the effectiveness of theinstant process for the depolymerization of tars, however, withoutlimiting the same.

EXAMPLE 1 A steam-cracked tar consisting of 35.7% material, boiling430-650 F., 34.3% boiling 650-1050 F., and 30% boiling 1050 F.+ wassubjected to two different cycles of hydrodepolymerization for fourhours each at different temperatures, one at 765F., and the other at 775F.

Tar feed, grams 456. 2 394. 3 Wt. percent tar 32. 8 32. 8 Wt. percent,650 F.recycle- 34. 0 34. 0 Wt. percent 650F.+recycle 33. 2 33. 2

n-Heptaue added to charge, grams 50. 1 50. 1

Operating conditions:

Avg. temp., F 765 775 Hours of run 1 2 4 Pressure, p.s

Maximum 1, 400 2, 000

Recoveries, grams:

n-Ileptanc 35. 4 30. 1 Liquid and gas ex. n-heptane:

C -gas l2. 7 23. 5 C 22l F. cut. 2. 5 3. 4 221650 F. cut. 2 260. 1 2213.5 650 F.+p0rti0n 186. 1 125.5 Coke 14. 4 33. 0

1 Autoclave was pressured to 1,000 p.s.i.g. with nitrogen prior to run.

2 Value does not contain small correction for possibly entrained 430-650F. vacuum flashing of tetrallne. Hence recoveries are not consideredcomplete and material balance not calculated.

The above data show that increasing the temperature increases the cokemake.

The present invention having thus been fully set forth and illustratedand specific examples of the same given, what is claimed as new, usefuland unobvious is:

1. A non-catalytic thermal process for producing coke and aromatic gasoil which comprises:

(a) introducing into a reaction zone 50 to wt. percent of a steamcracked aromatic tar, 20 to 50 wt. percent of a gas oil hydrocarbonfraction having a boiling point between 400 and 650 F., and 1 to 25 wt.percent of an acyclic hydrocarbon modifier boiling below said gas oilhydrocarbon fraction;

(b) operating the reaction zone at a temperature between 775 and 900 F.,and a pressure between 50 and 1000 p.s.i.g. to produce coke and aromaticgas oil, and

(c) recovering the coke and the aromatic gas oil.

2. The process of claim 1, wherein less than p.p.m. of oxygen based onsaid aromatic tar is added to the modifier before introducing in thereaction zone.

3. The process of claim 1, wherein a non-oxidizing gas is present insaid reaction zone.

4. The process of claim 3, wherein said non-oxidizing gas is hydrogen.

5. The process of claim 1, wherein said modifier remains in the vaporphase in said reaction zone for a residence time of about 5 to 60minutes.

6. The process of claim 1, wherein the modifier is a paraflin orisoparaffin hydrocarbon of 4 to 10 carbon atoms per molecule and wherein5 to 20 wt. percent of the modifier is introduced into the reactionzone.

7. The process of claim 6, wherein the modifier is nheptane or itsisomers.

8. The process of claim 6, wherein the modifier is nhexane or itsisomers.

9. The process of claim 6, wherein the modifier is n-pentane.

10. The process of claim 6, wherein the modifier is 2,2,4-trimethylpentane.

11. The process of claim 1, wherein the modifier is an olefin oriso-olefin hydrocarbon of 2 to 10 carbon atoms per molecule and wherein5 to 20 wt. percent of the modifier is introduced into the reactionzone.

12. A non-catalytic thermal process for producing coke and a gas oilhydrocarbon fraction boiling between 400 and 650 E, which comprises:

(a) introducing into a reaction zone 50 to 80 wt. percent of a steamcracked aromatic tar, 20 to 50 wt. percent of a gas oil hydrocarbonfraction boiling between 400 and 650 F., and 1 to 25 wt. percent of anacyclic hydrocarbon modifier boiling below said gas oil hydrocarbonfraction;

(b) operating the reaction zone at a temperature between 775 and 900 F.,and a pressure between 50 and 1000 p.s.i.g. to obtain a reacted mixture;

(c) removing a portion of said reacted mixture from the reaction zone;

(d) separating said portion of reacted mixture to obtain coke, a gas oilhydrocarbon fraction having a boiling point between 400 and 650 R, anacyclic hydrocarbon modifier boiling below said gas oil hydrocarbonfraction, and a hydrocarbon fraction having a boiling point above 650F.;

(e) recycling to the reaction zone the acyclic hydrocarbon modifier andthe hydrocarbon fraction having a boiling point above 650 F. along withthe necessary amount of the gas oil hydrocarbon fraction having aboiling point between 400 and 650 F. to insure the 20 to 50 wt. percentneeded in the reaction zone; and

(f) recovering the coke and the remaining portion of the hydrocarbonfraction having a boiling point between 400 and 650 F.

13. A non-catalytic thermal process for producing coke, a light gas oilfraction having a boiling point between 400 and 650 F. and a heavy gasoil fraction having a boiling point between 650 and 1050" R, whichcomprises:

(a) introducing into a reaction zone 50 to 80 wt. percent of a steamcracked aromatic tar, 20 to 50 wt. percent of a light gas oilhydrocarbon fraction having a boiling point between 400 and 650 F., and1 to 25 wt. percent of an acyclic hydrocarbon modifier boiling belowsaid light gas oil hydrocarbon fraction;

(b) operating the reaction zone at a temperature between 775 and 900 F.and a pressure between 50 and 1000 p.s.i.g. to obtain a reacted mixturecomprising coke, distillable hydrocarbon products, heavy residua-likehydrocarbon products and acyclic hydrocarbon modifier;

(c) removing a portion of said reacted mixture from the reaction zone;

(d) separating said portion of reacted mixture to obtain coke, a lightgas oil fraction having a boiling point between 400 and 650 R, anacyclic hydro carbon modifier boiling below said light gas oilhydrocarbon fraction, a heavy gas oil hydrocarbon fraction having aboiling point between 650 and 1050 F. and a hydrocarbon fraction havinga boiling point above 1050 F.;

(e) recycling to the reaction zone the hydrocarbon fraction having aboiling point above 1050" F. and the acyclic hydrocarbon modifiertogether with that portion of the hydrocarbon fraction having a boilingpoint between 400 and 650 F. necessary to maintain the 20 to Wt. percentin the reaction zone; and

(f) recovering the coke and the remainder of the hydrocarbon fractionhaving a boiling point between 400 and 650 F. and the hydrocarbonfraction having a boiling point between 650 and 1050 F.

14. The process of claim 13, wherein said modifier is a parafiin orisoparafiin hydrocarbon of 4 to 10 carbon atoms per molecule and wherein5 to 20 wt. percent of the modifier is introduced into the reactionzone.

15. The process of claim 13, wherein said modifier is an olefin oriso-olefin hydrocarbon of 2 to 10 carbon atoms per molecule and wherein5 to 20 wt. percent of the modifier is introduced into the reactionzone.

References Cited UNITED STATES PATENTS 2,717,865 9/1955 Kimberlin et al.208- 3,310,484 3/1967 Mason et a1. 208125 3,352,776 11/1967 Mason et a1.208-125 HERBERT LEVINE, Primary Examiner US. Cl. X.R. 208-50

